ListAdapter
public abstract class ListAdapter<T, VH extends RecyclerView.ViewHolder> extends RecyclerView.Adapter
| java.lang.Object | ||
| ↳ | androidx.recyclerview.widget.RecyclerView.Adapter | |
| ↳ | androidx.recyclerview.widget.ListAdapter |
RecyclerView.Adapter base class for presenting List data in a RecyclerView, including computing diffs between Lists on a background thread.
This class is a convenience wrapper around AsyncListDiffer that implements Adapter common default behavior for item access and counting.
While using a LiveData is an easy way to provide data to the adapter, it isn't required - you can use
submitList when new lists are available.
A complete usage pattern with Room would look like this:
@Dao interface UserDao { @Query("SELECT * FROM user ORDER BY lastName ASC") public abstract LiveData<List<User>> usersByLastName(); } class MyViewModel extends ViewModel { public final LiveData<List<User>> usersList; public MyViewModel(UserDao userDao) { usersList = userDao.usersByLastName(); } } class MyActivity extends AppCompatActivity { @Override public void onCreate(Bundle savedState) { super.onCreate(savedState); MyViewModel viewModel = new ViewModelProvider(this).get(MyViewModel.class); RecyclerView recyclerView = findViewById(R.id.user_list); UserAdapter<User> adapter = new UserAdapter(); viewModel.usersList.observe(this, list -> adapter.submitList(list)); recyclerView.setAdapter(adapter); } } class UserAdapter extends ListAdapter<User, UserViewHolder> { public UserAdapter() { super(User.DIFF_CALLBACK); } @Override public void onBindViewHolder(UserViewHolder holder, int position) { holder.bindTo(getItem(position)); } public static final DiffUtil.ItemCallback<User> DIFF_CALLBACK = new DiffUtil.ItemCallback<User>() { @Override public boolean areItemsTheSame( @NonNull User oldUser, @NonNull User newUser) { // User properties may have changed if reloaded from the DB, but ID is fixed return oldUser.getId() == newUser.getId(); } @Override public boolean areContentsTheSame( @NonNull User oldUser, @NonNull User newUser) { // NOTE: if you use equals, your object must properly override Object#equals() // Incorrectly returning false here will result in too many animations. return oldUser.equals(newUser); } } }
AsyncListDiffer, which provides custom mapping from diff events to adapter positions.
| Parameters | |
|---|---|
<T> |
Type of the Lists this Adapter will receive. |
<VH extends RecyclerView.ViewHolder> |
A class that extends ViewHolder that will be used by the adapter. |
Summary
Protected constructors |
|---|
ListAdapter(@NonNull AsyncDifferConfig<T> config) |
ListAdapter(@NonNull DiffUtil.ItemCallback<T> diffCallback) |
Public methods |
|
|---|---|
@NonNull List<T> |
Get the current List - any diffing to present this list has already been computed and dispatched via the ListUpdateCallback. |
int |
Returns the total number of items in the data set held by the adapter. |
void |
onCurrentListChanged(Called when the current List is updated. |
void |
submitList(@Nullable List<T> list)Submits a new list to be diffed, and displayed. |
void |
submitList(@Nullable List<T> list, @Nullable Runnable commitCallback)Set the new list to be displayed. |
Protected methods |
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|---|---|
T |
getItem(int position) |
Inherited methods |
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Protected constructors
Public methods
getCurrentList
public @NonNull List<T> getCurrentList()
Get the current List - any diffing to present this list has already been computed and dispatched via the ListUpdateCallback.
If a null List, or no List has been submitted, an empty list will be returned.
The returned list may not be mutated - mutations to content must be done through submitList.
| See also | |
|---|---|
onCurrentListChanged |
getItemCount
public int getItemCount()
Returns the total number of items in the data set held by the adapter.
| Returns | |
|---|---|
int |
The total number of items in this adapter. |
onCurrentListChanged
public void onCurrentListChanged(
@NonNull List<T> previousList,
@NonNull List<T> currentList
)
Called when the current List is updated.
If a null List is passed to submitList, or no List has been submitted, the current List is represented as an empty List.
| Parameters | |
|---|---|
@NonNull List<T> previousList |
List that was displayed previously. |
@NonNull List<T> currentList |
new List being displayed, will be empty if |
| See also | |
|---|---|
getCurrentList |
submitList
public void submitList(@Nullable List<T> list)
Submits a new list to be diffed, and displayed.
If a list is already being displayed, a diff will be computed on a background thread, which will dispatch Adapter.notifyItem events on the main thread.
submitList
public void submitList(@Nullable List<T> list, @Nullable Runnable commitCallback)
Set the new list to be displayed.
If a List is already being displayed, a diff will be computed on a background thread, which will dispatch Adapter.notifyItem events on the main thread.
The commit callback can be used to know when the List is committed, but note that it may not be executed. If List B is submitted immediately after List A, and is committed directly, the callback associated with List A will not be run.